1. Field of the Invention
This invention relates to a method of and an apparatus for injection speed control in a die-casting machine, utilized particularly for performing superlow speed injection employed for high quality die-cast molding.
2. Description of the Related Art
Heretofore, for obtaining forged metal products die-cast molding has been extensively utilized. In the die-cast molding, molten metal is injected into the cavity of a die by an injection plunger driven by an injection cylinder. The speed of injection is controlled by an injection speed control valve.
A usual die-cast molding is made by a standard injection process. In the process, at the beginning of the melt injection a low injection speed of about 0.3 m/sec. is set, and after the reaching of a die gate by the leading portion of the melt the injection speed is increased to about 3.0 m/sec. to quickly charge the melt into the cavity.
Meanwhile, high quality die-cast molding, for producing high mechanical strength, highly gas-tight forging, is made by a superlow speed injection process. In this process, a superlow injection speed of 0.01 to 0.5 m/sec. is set, and at the beginning of the injection the injection speed is set to 0.05 to 0.25 mm/sec. to prevent the melt in an injection sleeve from being cooled and solidified.
The standard and superlow speed injection processes have different injection speed ranges.
However, with the current injection speed control valves an extremely broad injection speed range can not be covered by merely changing the settings.
This means that the standard and superlow speed injection processes require respective exclusive injection speed control valves having different specifications.
However, installation of the exclusive die-cast machine for the individual injection processes poses problems in the installation space and installation cost. It is considered to install two different injection speed control valves in a single die-casting machine and switch these valves for the individual processes. Such a system, however, inevitably leads to complications of the control system and piping, making it difficult to elevate its utility.
An object of the invention is to provide a method of and an apparatus for injection speed control for a die-casting machine, which permit expansion of the injection speed control range of the injection speed control valve with simple means.